CO2 Drop Checker — Glass

The CO2 drop checker is the most reliable and widely used method for monitoring dissolved CO2 in planted aquariums. This borosilicate glass version features a classic inverted bell design that traps a small volume of aquarium water separated from the indicator solution by a small air gap, allowing CO2 to equilibrate between the aquarium and indicator without pH-affecting minerals or fertilisers interfering with the reading. Filled with 4dKH reference solution and bromothymol blue indicator dye, the fluid changes from blue (low CO2) through green (target 20–30 mg/L) to yellow (excessive CO2). The glass construction is inert and adds a refined visual element to the aquascape. Includes a suction cup for mounting inside the aquarium.